Ground speed meter



April 3, "1928.

s. H. ANDERSON GROUND SPEED METER Filed Jan.26. 1923 L I l 31 n j/w M J (Em-om? Patented Apr. I 3, 1928.

A 1,664,395 UNITED srnrss PATENT. o rrlca.

SAMUEL HERBERT ANDERSON, OF SEATTLE, WASHINGTON.

GROUND $PEED METER.

Application filed January 26, 1923. Serial no. 615,1;30.-

I This invention relates to ground speed indicators and more especially to such in which a revolving optical system isemployed to produce an apparent ground'velocity.

Heretofore in the art where rotating prisms were employed to produce avectorial addition of velocities in a plane parallel to the direction and surface of travel it had been proposed to rotate the entire optical system other than the prism system to obtain' an angular indication of the resultant drift produced in the field of. the eyepiece. Reference ,is made in this connection to Patent 1,299,058, grantedto C. A. Sundt.

As a consequence of the above method. of construction a good deal of fineness of adjustment was lost. The present invention in contradistinction inv'olvesa method of attaching the pointer for indicating angularity not directly to the cross hair \system' which had heretofore been made integral with the telescopic tube but rather to" an intermediate gearing meshing with the.

means for angularly'displacing the variable cross hair with res ect to a system of fixed cross hairs in the eld of the eyepiece.

As a consequence, of the above method of construction, it'nowbecomespossible to obtain a broadened outsca le" for calibrating the angular movement of the pointer both with'respect to altitude and resultant ground speed indicated. Q

In order more clearly to set forth the advantages and objects of the present invention the following drawings are attached in part sectional side constant speed of revolution. Between the objective 3 and the eyepiece 4 according to the inventionthereis mounted, first, a fixed cross hair system 4" relative to thetelescope body 1 and secondly, there is provided aring gear 5 revolubly mounted with respect to the telescope body or rather fixed cross hair system in such a. manner that an 'ex- 'ternal tangent screw 6 engages with the above ring gear which carries the variable set of cross hairs' The latter cross, hairs are, therefore, disposed to revolve in the plane of the ring gear and preferably in close contiguity to the fixed cross hairs 5 which are mounted in the ring gear 5.

In order to actuate the pointer 7 a second gear 8 in mesh with the tangent screw 6 is provided which is so arranged that on the actuation ofthe tangent screw, manually or otherwise, the pointer is made .to traverse an arc rather greater than the corresponding arc traversed by the ring gear 5 carrying the variable cross hairs5. The above magnification and simultaneous-fineness of adjustment made possible by=y. the above construction represents one of the rincipal advantages accruing to the prese *t invention. It will be understood that the prism 2"re.-; volves at aconstant speed on an axislongitudinal of the craft so as to cause an image of a sighted object to move, laterally across the field of view from one sideto the other,

disappear at the side toward which it moves,

and reappear again and repeat the action. The prism causes an artificial velocity of constant value and atha constant direction transverse of the aircraft. The travel of the aircraft forwardly actually is vectorially added to this artificial velocity to cause the apparent motion of objects to be at some angle to atransverse line and this angle is determined and registered by the pointer when the cross hairs 5 are aligned with the apparent motion.

With regard 'to thescale arrangement per se, in so far as it becomes necessary to correct for altitude at the same time as the .variable cross hairs need to be radiated to follow the resultant or compounded direction of the stream line effect, a series of curves 9 are drawn on the scale 10. Such curves are made to correspond with a ground speed scale 11 for different values of the altitude indicated by the circular coordinates '12. Thus, where for a given altitude circle 12 the pointer 7 passing through the point 7 (see Figure 3) strikes the corresponding curve of the familyqof curves 11 there will be automatically selected one of such family of curves 11, which will give the proper coordinate value of the actual ground speed. I

In operation, therefore, through the eyepiece 4 the tangent screw 6 on looking is so varied till coincidence of the variable cross hairs. with the resultant stream line is effected. The needle 7 with respecttothe scale 10 will then give the proper indication of the ground speed for the-previous- 1y known altitude.

Having disclosed 1; A ground speed lndicator comprisin I a scale and mounting therefor, a revolu le' cross haifgear device on said-mounting,

and a pointer gear device,.on said mounting for cooperation with said scale'and an adthe nature of. my invention what I claim is 3 digsting tangent screw means in mesh with th said gear devices, said scale including 15 altitude and ground speed coordinates. for variable settings ofsaid' pointer device.

2. A ground speed indicator comprising a telescope body. having a ring gear carrying cross airs revolubly mounted therein-,' :a 2'0 pointer havinga gear thereon and actuatin means includlng a worm means in mes with said ring gear and saidsecond'ment ioned gear. 1

In testimony whereof I aflix my signature.-

SAMUEL HERBERT ANDERSON." 

